In steel mills, hot molten steel is formed into slabs in a hot steel slab caster section. In continuous slab casters, molten steel enters a formation chamber. One or more steel slabs emerge from the formation chamber with a thin skin of solidified steel holding them together. These freshly formed steel slabs are conveyed away from the formation chamber on suitable material moving means. The temperature of these slabs in this section of the steel mill is typically in the range of 900° C. Non-fire resistant grease based on petroleum, vegetable, or synthetic oil would ignite if it came in contact with the slabs. Thus in steel mill applications, especially in the continuous casting section, fire resistant greases are preferable to non-fire resistant greases.
As noted above, a problem associated with non-fire resistant steel mill greases is the possibility of grease fires. Grease fires can occur from hot molten metal, from acetylene torches during periodic maintenance, and from other sources of ignition. It is highly desirable to have high performance steel mill greases which also reduce the occurrence of grease fires.
The ability of grease compositions to be more fire resistant should be instilled in the grease composition without degradation of the necessary lubricating features for which the grease composition is intended.
According to Hackh's CHEMICAL DICTIONARY, Fourth Edition, Page 307, grease is defined to be oil thickened with soap. For the purposes of this specification, a conventional grease is grease which is not necessarily modified for improved fire resistance, and is defined as grease which comprises base oil and at least one grease thickener. Conventional grease may also comprise additional components and additives. For the purposes of this specification, a grease composition designated as having fire resistance or improved fire resistance is defined as a grease composition which possesses at least one of the two following qualities: (1) the grease composition will not spontaneously ignite (burn with flames) at the intended surrounding service temperature, that is the grease composition will not ignite for example on contact with surfaces having temperatures of up to 900° C., (2) if the grease composition does ignite, the flames will self-extinguish within a predetermined time period. Unless otherwise specified, the predetermined time period will be five minutes for the purposes herein.
The need for improved fire resistant lubricating grease compositions, especially those that are fire resistant at temperatures higher than the prior art, has been the subject of research and patent activity over the years and such activity continues to this date. U.S. Pat. No. 4,206,061 of Dodson et al. and U.S. Pat. No. 5,128,067 of Douglas G. Placek relate to fire resistant phosphate ester based greases. The greases, as described in these patents, are limited in base oil viscosity as required by the bearing speed and size. Also, under the application conditions, the phosphate ester may be subject to hydrolysis in the presence of water leading to a premature degradation of the grease, resulting in poor lubrication that will cause a reduction in the bearing service life. One grease composition of U.S. Pat. No. 4,206,061 of Dodson et al did not spontaneously ignite when placed on a hotplate held at 650° C. (column 4 at lines 31-34).
Laid open Japanese patent applications having document numbers JP2004067843 and JP2006225597 relate to conventional greases with high base oil flash points of 270° C. minimum (English abstract of JP2004067843; Page 3 of the machine translation for JP2006225597) and high viscosity (300 cSt minimum at 40° C.). The greases of these patent applications are described as self-extinguishing or fire retardant greases. These applications relate to grease compositions that may ignite but do not sustain the flame for durations longer than five minutes as per a fire resistance test described in these two publications.
Laid open Japanese patent application having document number JP2002146376 relates to conventional greases which further comprise a water absorptive polymer and water. This publication further reports that these additional components provide fire resistance properties to the greases. This publication further reports that the greases of this invention do not ignite at temperatures as high as 500-600° C. (see English language abstract). However, this laid open application goes on to indicate that the lubricity of the greases is compromised as water is released from the absorptive polymer during normal service life of the grease.
Laid open Japanese patent application having document number JP2007277459 discloses greases based on phosphate esters, mineral oils, polyalphaolefins (PAOs), or combinations thereof, and various thickening systems including calcium sulfonates. This published application reports that the greases do not ignite, according to a modified fire resistant test method, at temperatures up to 950° C. provided the greases comprise at least 71 weight percent phosphate esters (paragraphs 0015 and 0040 of machine translation).
According to U.S. Pat. No. 3,242,079 of Richard L. Mc Millen a substantial amount of water (or water/alcohol mixture) is employed in the preparation of a grease composition which comprises calcium sulfonate among other required ingredients. However, in Example I in column 6, the grease is heated and blown dry leaving no water in the final grease composition.
The documents referred to above on the subject of fire resistant grease compositions show that research and patent activity in this area of technology are still active areas of investigation. Higher performance and/or more economical fire resistant grease compositions are needed and in demand. This invention represents further effort and advancement in development of high performance, safe, low cost, fire resistant grease compositions.